Importance of Overlooked Crop Biomass Components in Sugarcane Nitrogen Nutrition Studies
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsLine 108 - planted in 2014, yet Figure 1 shows 2018 and 2019
Line 110 - state that "6 treatments, each with a different fertilizer" were used. Yet, those treatments are not addressed anywhere in the Results or Discussion that I could find. Where those different treatments lumped for the analyses, since you only report fertilized and un-fertilized? If so, you may have committed pseudoreplication and further compounded the statistical issues listed below.
Line 143 - Strawfall sampling from catchment - what about controlling for wind. In other words, how do you know that dry leaves weren't blown off the catchment nets and missed...
Figure 1 - suggest removing graph lines from t=0 to date of first sampling. To me, that presupposes your straight lines are representative, and you have no data to support it. Additionally, this differs from Figure 2, where the graph lines start at t>0. By using the logic shown in Figure 1, you should also have the tillers at 0 at t=0, but I'd prefer the approach of Figure 2 over Figure 1.
Lin 245 - you state that strawfall biomass and N mass were higher over the second experimental year than the first, yet Figure 3 shows the opposite.
Sections 3.1, 3.2, 3.3, 3.4, 3.5, and 3.7 - you state that some values are higher than others, and yes, numerically they appear to be, but the error bars on the graphs appear to overlap in many cases, and you've cited no statistical results to show that there actually is a significant difference.
Section 3.6 - need more details on the statistical analysis. It would appear that time was used as a blocking factor in the ANOVA, yet that was not included in Section 2.7 detailing the stats used. Also, where are the results of Tukey's test? You state there are significant differences between components and time, yet didn't provide those results. Also, with so little details provided on the statistical setup, I'm concerned about a lack of independence between observations since time is included. Is biomass at time t affected by biomass at time t-1? Probably. See Figure 1 (left-hand graph). The same could be said for N mass. There is a possibility that some of the conclusions (like the paragraph starting at line 506) might be affected once the statistical results are taken into account. For example, you state that "tiller component can lead to a decrease in the dNRE...", but if those differences are not found to be statistically significant, then that statement might not be valid.
Line 454 - should provide levels for the standard which you are comparing against. What constitutes high or low values for NRE?
Author Response
Please see the attached file. Thank you for your thorough review and insightful comments. We have tried to incorporate these points as best as possible into the manuscript, and have responded to each of the comments in the attached PDF.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Editor,
it was my pleasure to review such a well written paper. Overall, it is written in very good English, provides an adequate literature review and clear formulation of the research questions in the introduction, good presentation of the results, detailed discussion and conclusions based on the results.
However, there are some points that need correction or clarification.
Introduction.
line 43-44. NRE is not a quantification index of NUE. It's a different indicator. It can be written that it is a component of NUE or that it co-varietes. Please correct and not use the term NUE in the entire introduction as it has not been calculated from the measurements and is not presented in the results. Use only NRE.
Methods and materials.
a) Plant density in the experimental plots is not reported. Only the distances between the lines are reported. The results (Figure 2A) show a different number of cane number per m2 for the fertilised and unfertilised plot. Why is this happening; Authors must provide explanations for the difference plant population since it affects all their measurements and comparisons.
b) line 116-117. Why has a different N rate been applied in the second year? Why is there a one month difference in application?
c) No information has been given on the initial fertility of the soil. Data from a basic soil analysis are essential in such work.
d) Fertilization application data for P and K have not been provided. Combined with the lack of soil analysis data for the levels of these nutrients in the soil, they weaken the conclusions about the exclusive effect of N on the measured quantities (e.g. aboveground and belowground biomass ).
Discussion
lines 436-442. The authors should include the effect of residual N in the soil. The existence of residual N is predicted by their own data and the low NRE of the fertilizer they applied as main fertilization and after the first growth cycle as well. Please rephrase or remove the theoretical scenario.
Author Response
Please see the attached file. Thank you for your thorough review and constructive comments. We have tried to incorporate these points as best as possible into the manuscript, and have responded to each of the comments in the attached PDF.
Author Response File: Author Response.pdf
